1. Field of the Invention
The invention is directed to a polymer shim and a roll-to-roll process for its manufacture.
2. Description of Related Art
Image embossing tools have been disclosed previously. U.S. Pat. No. 4,923,572 (hereinafter referred to as the '572 patent) discloses a generally cylindrical image embossing tool which can be used for embossing a material on a web. The method for the manufacture of the image embossing tool involves multiple steps, including (1) placing an embossable material around the surface of a rigid cylinder, (2) stamping a desired image or pattern onto the embossable layer with a stamper, (3) electroforming to form a nickel electroform on the outer surface of the embossable layer, (4) applying a reinforcement layer over the electroform, (5) removing the rigid cylinder; (6) stripping the embossable layer to form a plating mandrel, (7) forming a second electroform by electrodeposition of a metal on the interior of the plating mandrel and (8) removing the second electroform. According to the '572 patent, multiple copies of the second electroform can be prepared in the same manner and they may then be placed over a carrier cylinder or a plurality of rollers to form an embossing tool to allow continuous embossing. This embossing tool and its manufacturing process, however, suffer many disadvantages. For example, the process requires a cylindrical or belt type of embossing tool and the stamping surface of the stamper must have a curvature corresponding precisely to the curvature of the embossable material on the rigid cylinder. This is difficult to accomplish in practice. Secondly, both the first and second electroforms are of a metal material such as Ni. It may be difficult to separate the two electroforms in the cylinder form, particularly when a complex structure of a high aspect ratio is to be duplicated. In addition, if a cutting step is involved in the separation of a metal shim, it will be difficult to rejoin the pieces to form a seamless embossing cylinder or drum. Furthermore, it is very difficult to maintain a uniform and precise surface profile if the shim to be formed by this process has a steep 3D profile such as a depth of larger than 10 um and an incline angle of less than 10°.
U.S. Pat. No. 5,327,825 (hereinafter referred to as the '825 patent) discloses a method for forming a die through embossing or microembossing. More specifically, the method involves embossing a pattern or design onto a silver layer coated on a cylindrical surface, via the use of a concave shaped stamping surface which carries the pattern or design to be imparted onto the silver layer and has a radius matching the radius of the cylindrical surface. This microembossing step is carried out multiple times so that the die prepared from the method has a repeated pattern or design from the concave-shaped stamping surface. This method has disadvantages similar to those of the process of the '572 patent (e.g., difficulty in matching the radii of the stamping surface and the cylindrical surface, maintaining precise and uniform surface profile and the formation of a seamless tool for complicated structures, particularly those with a deep 3D profile).
U.S. Pat. No. 5,156,863 (hereinafter referred to as the '863 patent) discloses a method for manufacturing a continuous embossing belt. The method involves combining a series of “masters” or “copies” in a cluster to provide a desired pattern in a fixture and an electroform strip is formed of the cluster. The embossing belt is formed after multiple electroforming steps starting from a master cluster fixture. One of the drawbacks of this method is the difficulty to generate the individual masters or copies for the cluster with a uniform height (or thickness). In addition, a grinding step is required in this method to eliminate surface imperfections. It is also difficult in this method to avoid damage on the mandrel and shim during separation of the electroformed nickel shim from its nickel mandrel, particularly when a complicated structure with a deep 3D profile is involved.
Furthermore, all of the processes discussed above can only produce one embossing tool at a time.